Over the years skid steer loaders have been known as agile, compact vehicles with a high degree of maneuverability and a wide range of applications in the agricultural, industrial and construction fields. These vehicles usually include an engine, a boom assembly and an operator compartment mounted on a frame supported by four ground engaging wheels. Coupled to the engine are a main drive system and a lift system for the boom assembly. The vehicle is maneuvered by driving the wheels on one side at a different speed and/or in a different direction from those on the other side resulting in a turning motion, the severity of which is determined by the relative speeds.
Typically the engine, which is rear mounted for counterbalancing effect, drives a pair of hydrostatic pumps coupled to left and right mounted hydrostatic motors. Wheels on the left and right sides of the vehicle are driven by the left and right mounted motors through gears, chains and sprockets. Motion is usually controlled by an operator seated within the operator compartment by actuating a pair of control levers which are linked to the pumps. The extent to which each lever is moved in a forward direction from a neutral position controls the amount of fluid supplied in a forward direction to its respective motor, and therefore the speed at which the wheels on that side of the vehicle will rotate. Similarly, the extent to which a lever is moved in the reverse direction from the neutral position will control the speed at which the associated wheels rotate in the reverse direction.
As mentioned above, skid steer loaders include a boom assembly, which consists of a pair of lift arms pivotally mounted on the main frame or a support frame extending upwardly from the main frame as shown in U.S. Pat. No. 3,903,978, issued Sep. 9, 1975 in the name of Peter B. Kraus. Material handling attachments, such as the bucket 18 shown in this patent, are usually mounted on the front of the lift arms. U.S. Pat. No. 4,892,155, issued Jan. 9, 1990 in the name of Richard B. Wanamaker, is also representative of skid steer loader type vehicles having lift arms supported on the main frame.
Another well known arrangement found in vehicles of this type comprises a pair of lift arms coupled to the frame by means of a linkage assembly, as best illustrated by U.S. Pat. No. 3,215,292, issued Nov. 11, 1965 in the name of Lawrence M. Halls. This linkage arrangement enhances the path of the bucket by moving it outwardly from vertical as it rises. Similar skid steer loader linkage systems are disclosed in U.S. Pat. Nos. 3,995,761, issued Dec. 7, 1976 in the name of Joseph C. Hurlburt and No. 4,355,946, issued Oct. 26, 1982 in the name of Lloyd A. Wykhuis, et al.
In a recent improved loader mechanism in which the boom assembly utilizes a linkage system similar to those referenced above, the lift arms are supported by the vertical walls of the cab. Exemplary of an assembly of this nature is the skid steer loader boom assembly shown in U.S. patent application Ser. No. 08/293,945, filed on Aug. 24, 1994 in the name of Dale A. Ashcroft, et al, and assigned to a common assignor.
A separate hydraulic system is usually used in skid steer loaders to power the boom assembly via hydraulic lift cylinders coupled to the lift arms. This same system can also be used to actuate one or two tilt cylinders which pivot the attachment relative to the lift arms, which is commonly referred to as dumping or curling the attachment. A pair of foot pedals in the front of the operator compartment control the flow of hydraulic fluid from a hydraulic pump to the lift and tilt cylinders.
In addition to material handling buckets, various other attachments, such as snow blowers, trenchers, tree spades and augers, which may include their own hydraulic motors and/or cylinders, are commonly mounted to the boom assembly. An auxiliary hydraulic system is used to control the flow of hydraulic fluid between a pump and the hydraulic motor of front mounted attachments. It is common in prior art systems for the flow of hydraulic fluid to the motor to be controlled by an auxiliary spool valve through actuation of a handle on one of the control levers. The handle is normally biased to a neutral position. Pushing the handle in one direction strokes the auxiliary valve in a first direction, thereby causing hydraulic fluid to flow in a first direction to such front mounted attachment. Pushing the handle in the opposite direction strokes the auxiliary valve to supply fluid in a reverse direction.
Of the wide range of attachments used in conjunction with skid steer loaders the most common is a material handling bucket mounted to pivot relative to the lift arms. The bucket is operational over its full lift path, e.g., it is positioned to receive a load while resting on or in the vicinity of the ground, after which it is pivoted upwardly and raised to an intermediate position for transport to a remote unloading area where it is unloaded by pivoting it downwardly to discharge its contents. Unloading may also take place at various elevated bucket positions relative to the loading or transport positions for discharging into the back of a dump truck, over the side of a manure spreader, etc.
A problem common to skid steer loaders is excessive noise encountered by the operator. Engine and hydraulic drives typically generate high levels of noise that travel to the operator via external as well as internal airborne paths. The noise also travels from the source to the operator via paths that are structure borne. In the past the structure borne paths that originate at the engine and transmission compartments have been interrupted by isolating the cab from vibrations of the main frame or chassis. For example, U.S. Pat. No. 4,150,474, issued Apr. 24, 1979 in the name of James J. Bauer, et al, shows in FIG. 12 a skid steer loader in which rubber cushions are mounted between the operator's compartment and the main frame of the vehicle.
There have also been attempts to reduce the affect of airborne noise by use of a cab in which the operator is enclosed by windows and doors to prevent airborne noise from entering the operator's work area. However, structure borne noise is still trapped in the enclosure and it can only be dealt with by use of ear protection which is less than desirable to an operator.
Applicants have learned that the boom structure in skid steer loaders is a significant noise transmission source for structure borne noise, under conditions where the boom is mounted to the chassis. Even when the cab is isolated (as mentioned above) this source of noise continues to be troublesome because the noise path is structurally coupled to the boom assembly which operates in paths adjacent to and in the vicinity to the operator.
Some government agencies and various European countries require that vehicles, such as skid steer loaders, must meet noise level standards that are difficult to achieve in a cost effective manner while still providing an "operator friendly" environment. For example, by installing doors and windows to interrupt external airborne noise the operator is inconvenienced by reducing flow of fresh air as well as the added task of opening and closing the door during each entrance and exit. Also, the use of ear protection devices to meet standards necessitates removal and storage each time the operator shuts down the machine, not to mention the added cost, discomfort, etc.
In all known prior art apparatus of which applicants are aware there is no skid steer loader cab mounting apparatus that provides for optimum noise isolation by isolating the cab and boom structure by common means.